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1) Problem Statement

1) Problem Statement Puzzling questions concerning troubleshooting electric motors performance and troubleshooting. 2) Lesson Learned Was able to compile information to assist in determining the effects of voltage on motors and troubleshooting tips. Motor Volts & Amps.

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1) Problem Statement

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  1. 1) Problem Statement • Puzzling questions concerning troubleshooting electric motors performance and troubleshooting. • 2) Lesson Learned • Was able to compile information to assist in determining the effects • of voltage on motors and troubleshooting tips.

  2. Motor Volts & Amps • Part of a Compressor “Start-up” is checking and recording incoming VOLTAGE and motor “FULL LOAD AMPS” • Also when troubleshooting “MOTOR OVERLOAD” trips or faults, Blown fuses, or tripped breakers, we also check VOLTAGE and AMPS. • So what is “GOOD” voltage and amperage?

  3. Causes of high amperage • Or VOLTS & AMPS they go together. • Electric motors convert electrical energy into mechanical (rotating) energy or motion. So the more work a motor is required to perform the more the more electrical power (current) is required. When motors are manufactured, the field windings (copper wire) are extremely close in length and there is a consistency of material throughout. Therefore a motor with un-damaged internal components operating with consistent load will use equal (or very close to) current on all 3 legs.

  4. SAFETY • The voltages in a compressor’s electrical system can be LETHAL. • ONLY PERSONS PROPERLY TRAINED AND FOLLOWING PLANT OR APPROVED PROCEDURES SHOULD PERFORM TESTS ON ELECTRICAL EQUIPMENT. ONLY USE TEST EQUIPMENT THAT IS IN GOOD WORKING ORDER.

  5. Are the amps really high? • Compressor manufactures design equipment to operate using the Service Factor of the motor. Check the motors’ nameplate and calculate Maximum Amperage by multiplying the “nameplate” Amperage by the Service-Factor.

  6. Are the amps really high? • Check for proper operation and settings of the compressors controls. • One of the most frequent causes of “high amp draw” is operating the compressor at higher pressures than designed, or the modulation portion of the compressors’ controls are not properly adjusted.

  7. Are the amps really high? • Confirm readings are accurate. • An article in the Department of Energy publication “Energy Matters” (fall 2001) notes that when using “clamp-on” current transformers, there will be inaccurate readings if the jaws of the amp clamp do not fully close. In there testing a .004 inch gap separating the jaw faces resulted in a reading of 78 amps on a 100 amp load. (An indication that the jaws are not fully closed or aligned is “buzzing” felt in the clamp).

  8. Are the amps really high? • Check voltage “Line” to “Line”. • Checking “Line” to “ground” will likely only confuse you. Since motors' windings are connected Phase to Phase, Line to Ground voltages have no effect on the motor. If a motor failure is suspected a megger or other motor testing device should be used. Generally internal shorts to ground or phase to phase show themselves dramatically.

  9. Are the amps really high? • Is the voltage high or low? • The nameplate on a motor includes: Voltage, Full Load Amps, & Service Factor ratings. • Standard Voltages for most motors used in the United States are rated for 230 & 460 Volts. • By N.E.M.A. standards the voltage can vary by + / - 10%. • So: • 10% of 460 Volts is 46 Volts, • MAXIMUM voltage would be 506 volts (460 + 46) • MINIMUM voltage would be 414 volts (460 – 46). • 10% of 230 Volts is 23 Volts, • MAXIMUM voltage would be 253 volts (230 + 23) • MINIMUM voltage would be 207 volts (230 – 23). • Generally speaking, these variations were established to accommodate normal “hour-to-hour” swings in a plants voltage. Operating continuously at the high extreme or the low extreme will shorten the life of the motor, and can result in tripping of protective devices.

  10. But what happens when a motor is operated at deviations from rated voltage ? • When motors are operated below rated nameplate rated voltage, changes occur, some slight and others more significant. The bottom line is; for a motor to drive a fixed load, a fixed amount of power is required. The amount of power used by the motor is roughly related to voltage x amps. So if volts are low, amps must be higher to produce the same work. Therefore; if voltage is 5% lower than nameplate rating, the amps will also increase by 5%. This higher amperage results in higher temperature in the motor. • Also low voltage will DECREASE “starting torque”, “pull up torque”, and “pull out torque”. The reduction in torque is equal to the applied voltage squared.

  11. Low Voltage Examples: • 5% reduction in voltage (460 volts to 437 volts) will decrease starting, pull up and pull out torque by a factor of .95 x .95 (95% of rated voltage). The result will be 90.25% of rated torque. • 10% reduction in voltage (460 volts to 414 volts) will decrease starting, pull up and pull out torque by a factor of .9 x .9 (90% of rated voltage). The result would be 81% of rated torque. • So low voltage not only results in higher amperage with an increase of motor heat, it also reduces torque, leading to hard or slow starting motors.

  12. High Voltage • If low voltage is bad, and results in proportionally higher amperage, then high voltage will result in lower amperage. • This is only true to a point. As voltage increases, near the maximum, the magnetic portion of the motor is forced into saturation. This results in the motor pulling higher amperage in an effort to magnetize the iron beyond the point which it is easily magnetized. The results are excessive heating, and shorter motor life.

  13. High Voltage There is no “rule of thumb” for calculating the effects of high voltage to amperage increase. Some motors tolerate higher voltage better than others. But, high voltage (above nameplate ratting) will result in; • Higher inrush current • Reduced full load efficiency • Higher internal temperatures (shorting motor life). • Reduction in Power Factor

  14. Voltage Imbalance: (a leading cause of high Amperage and reduced motor life) • Voltage imbalance is defined by NEMA (National Electrical Manufactures Association) as: “100 times the absolute value of the maximum deviation of the line voltage from the average voltage on a 3 phase system, divided by average voltage”.

  15. Voltage Imbalance • To calculate: To calculate: • Measure the “line voltage” (L1 - L2, L2 – L3, L3 – L1) • Find the AVERAGE voltage (sum of the voltage measured on the 3 lines ÷ 3) • Find the MAXIMUM DEVIATION from average (measured line voltage that is greatest from average.) Subtract the MAXIMUM DEVIATION from the AVERAGE. • Divide the MAX DEVATION by the AVERAGE and multiply the sum by 100.

  16. Voltage Imbalance / calculation example 1. Measure the “line voltage L1 - L2 = 449 Volts, L2 – L3 = 470 Volts, L3 – L1 = 462 Volts 2. Find the AVERAGE (449 + 470 + 462 Volts = 1381), (1381÷ 3 = 460 average) 3. Find the MAXIMUM DEVIATION / Subtract the MAXIMUM DEVIATION from the AVERAGE. 449 volts is the greatest deviation from 460 (average volts) 460 – 449 = 11 Volts 4. Divide the MAX DEVATION by the AVERAGE and multiply the sum by 100 (11 ÷ 460 = .0239) then (.0239 x 100 = 2.39) PERCENT IMBALANCE = 2.39%

  17. Effect of voltage imbalance • Again there is no definitive rule for amperage increase based on voltage imbalance. • A U.S. Department of Energy (DOE) paper on motor voltage imbalance reports a 2.5% voltage imbalance in the feed to 100 h.p. motor resulted in a 27.7% current (amperage) imbalance. • The same DOE article noted that voltage imbalance will cause a motor to run hotter. The additional temperature rise (in degree C) is estimated with the following equation: • Percent additional temperature rise = 2 x (% voltage imbalance)². • Therefore: 2% voltage imbalance would result in an 8% temperature rise. 2 x (2%)² • So: A motor with a 100° C temperature rise would experience a temperature increase of 8° C (8% of 100°). The result of the higher temperature is; winding insulation life is reduced by one-half for every 10° C increase in operating temperature. • Another article noted that “a 1% voltage imbalance will result in a 6% -10% current increase. While other articles note that between 2% to 4% imbalance is the maximum that can be tolerated.

  18. TROUBLESHOOTINGMotor overloads trip, fuses blow, or circuit breakers open consistently CHECK: • The compressor controls are properly operating and adjusted. • Fuses / Circuit breakers are properly sized, rated, and adjusted (circuit breakers). • Overload heaters are properly sized (and set properly if adjustable), and correctly installed. (Remove, inspect, and reinstall the overload heaters). • Is the voltage at the high or low limit? Calculate voltage imbalance. • Check the surrounding temperature at the overload block area. Extremely high ambient temperatures will affect the overload heaters. • That all electrical connections are properly tightened.

  19. TROUBLESHOOTINGIf the FAULT occurs “once in a while” CHECK: • Do the trips occur at given times (i.e. right before lunch, only at night, on weekends)? If the above have been checked, suspect fluctuations in the customer’s electrical supply. Observation: MOTORS DO NOT GO BAD SOME OF THE TIME (LIKE ON EVENINGS OR WEEKENDS). Once a motor starts to electrically fail, it will continue to fail rapidly. Motors normally do not devolve phase to phase shorts, same phase shorts or phase to ground faults “some of the time”.

  20. TROUBLESHOOTINGIf the over current protection device “trips” when the compressor is starting. Check: • Is the device (fuse, circuit breaker, overload heater) properly sized and adjusted. • Some solid state circuit breakers have “ground fault” monitoring built into the device. This works by comparing the current between all phases, and “trips” if there is an in-balance (what goes out has to come back). When starting a loaded motor there may be a very short in-balance, which could cause a solid state breaker to trip. Normally, breakers with ground fault monitoring can be adjusted to compensate for this condition. • Is the voltage at the high or low limit? • Is the compressors’ air-end filling with lubricant? Malfunctioning compressor components can allow lubricant to fill the air-end on shut-down. If there is significant lubricant in the air-end starting will require higher than normal torque. • If the compressor is equipped with closed inlet starting and is it functioning properly? The purpose of closed inlet starting is to reduce the “load” during starting. It is mostly used on compressors with “reduced voltage” starters. • Is the voltage extremely high or low? • Is the motor connected for the proper voltage?

  21. OBERSVATIONS • High Voltage: Almost always a problem with the electrical supply system. It could be that transformer(s) need re-tapped, or transformers are lightly loaded. This should be corrected by the customer, and noted on reports. • All lines have low voltage: • Compressor not running: the likely problem is with the customers’ electrical system. This should be brought to the customer’s attention and corrected before the compressor is placed in service. • Voltage drops when the compressor is running: If the voltage drop is significant and is equal on all 3 lines, suspect undersized wiring in the plant distribution system. • Check elsewhere in the plant for low voltage on other equipment. • One or two lines drop low when compressor is running: • Suspect a bad connection. This could be on the Customers’ side or on the Compressor side. Confirm all connections and lugs are tightened to the proper torque. This includes all starter and motor connections. • Check other equipment in the plant for “low voltage lines”, it could be that the plants electrical load is imbalanced and the extra load from the compressor is causing a “system” imbalance.

  22. OBERSVATIONS • One or two lines drop low when compressor is running: • Try rotation the incoming lines (A to B, B to C, C to A). Check rotation before proceeding. If the low voltage follows the change, suspect problems in the “customer (supply) side”. • If the “low voltage lines” (or high amperage lines) “stay with the motor” • RE-CHECK the incoming and motor lugs on starters. • RE-CHECK the connections at the Motor Terminal Junction Box. • Check for voltage drop across the starter. Using a digital voltmeter check from the “Line lug” to the same phase “Motor Lug”. Voltage drop should be similar on all 3 phases and normally < .5 volts. If higher voltage drop is detected, check: lug tightness, overload relays for correct seating and tightness, starter contacts. • Have the motor tested.

  23. NOTES ABOUT MOTOR STARTERS • Motor starters (contactors) are electro-magnetic devices that use a magnetic field to engage movable contacts with stationary contacts, completing a circuit from the line to motor. Most starters have a button or indicator for the position of the armature that supports the movable contacts. IT IS NOT A SAFE PRACTIACE TO MANUALLY ENGAUGE A STARTER BY PRESSING ON THE BUTTON OR INDICATOR. CONSIDERABLE MAGNETIC FORCE IS GENERATED BY THE COIL IN THE STARTER, AND IT IS UNLIKELY THAT THIS FORCE CAN BE DUPLICATED BY HAND. ALSO AS THE CONTACTS “MAKE” (CLOSE) OR “BREAK” (OPEN) AN ARC IS CREATED THAT IS VERY HOT. DO YOU WHANT YOUR FINGER OR BODY PARTS IN CLOSE PROXAMITY TO A DEVICE THAT COULD POSSIBLY EXPLODE OR ELECTRICALLY MELT? DON’T DO IT!! The contacts used in motor starters are “silver cadmium oxide alloy”. It is normal for contacts to “dark, rough, or pitted”. Starter contacts’ should not be filled or dressed.

  24. NOTES ABOUT MOTOR STARTERS • ALSO, during start-up or service look over the starter(s) and other components for metal “chips” created when holes were drilled in the cabinet to install conduit or other devices. Also looks for small pieces of wire insulation or other foreign material laying on the starters or other components. • IF METAL “CHIPS” OR INSULATION PICES ARE NOTED, DO NOT APPLY POWER TO THE SYSTEM OR ATTEMPT TO START THE COMPRESSOR. DISSASEMBLE THE STARTERS, BLOW, VACUUM OR OTHERWISE REMOVE ALL FORGIN MATERIAL. IF A SMALL PIECE OF MATERIAL LODGES BETWEEN A STATIONARY AND MOVABLE CONTACT, THE CONTACTS MAY BURN, MELT OR “WELD” TOGATHER.

  25. NOTES ABOUT MOTOR STARTERS • WHEN WORKING ON ELECTRICAL SYSTEMS, ALLWAYS “LOCK-OUT” AND TEST BRFORE TUOCHING ANYTHING. EVENTHOUGH A MOTOR IS NOT RUNNING AND THE “BUTTON” ON THE STARTER IS INDICATING THE STARTER IS “OPEN”; A SET OF STARTER CONTACTS COULD BE “WELDED”, WITH LINE VOLTAGE AT THE BOTTOM OF THE STARTER AND AT THE MOTOR. • ALSO SOME SOLID STATE STARTERS AND ALL VARABLE FREQUENCY DRIVES HAVE CAPICATORS THAT STORE ELECTRICAL ENERGY. LEATHAL VOLTAGES CAN BE PRESENT EVEN WITH THE DISCONNECT OPEN. • TEST BRFORE TUOCHING!

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